Hund’s Rule is a simple principle about how electrons fill orbitals of the same energy (called degenerate orbitals).
Rule:
- Every orbital in a given sublevel (like p, d, or f) gets one electron first before any orbital gets a second electron.
- All single electrons in these orbitals have the same spin.
Why:
- Electrons repel each other, so they stay unpaired as much as possible to minimize repulsion.
Example:
For carbon (1s² 2s² 2p²):
- The 2p sublevel has 3 orbitals.
- Hund’s rule says: place one electron in each of two 2p orbitals before pairing them.
Visual:2p orbitals: ↑ ↑ _
- Each ↑ represents a single electron with the same spin.
In short:
“Electrons occupy empty orbitals first, with parallel spins, before pairing up.”